Conventional radio-frequency heating apparatuses typically include a radio-frequency power generation unit constituted of vacuum tubes called magnetrons.
In recent years, radio-frequency heating apparatuses that include, instead of the magnetron, a semiconductor device such as GaN have been developed (for example as seen in PTL 1). Such radio-frequency heating apparatuses can be made smaller in size in lower cost, yet allow frequency and phase to be easily controlled. PTL 1 discloses a technique of controlling the frequency and phase difference of radio-frequency power radiated from a plurality of radiation units so as to minimize reflected power, to thereby heat an object in a desirable state.